Glasses for temperature-stable ultrasonic delay lines of low damping characteristics

ABSTRACT

GLASS COMPOSITIONS FOR USE IN DELAY LINE ASSEMBLIES HAVING LOW TEMPERATURE COEFFICIENT OF PROPAGATION TIME FOR ULTRASONIC WAVES, LOW MECHANICAL DAMPING, A TRANSFORMATION TEMPERATURE OF ABOUT 540-600*C. AND HIGH ACCOUSTICAL IMPEDANCE. PREFERRED COMPOSITIONS IN PERCENT BY WEIGHT ARE AS FOLLOWS:   SIO2 48.5-49.7 LI2O 0-0.2 NA2O 0-0.6 K20 0.7-1.0 BAO 10.5-11.5 ZNO 3.1-5.8 PHO 3.1-34 SB2O3 0.3-0.5   THE TOTAL ALKALI METAL OXIDE AMOUNTING TO 0.7-1.8%, WITH THE PROVISO THAT UP TO 2 OF THE WT. PERCENT OF BAO MAY BE REPLACED BY CDO, SRO, CAO, WO3, AL2O2, OR A MIXTURE OF TWO OR MORE THEREOF, FOR STABILIZATION AGAINST DEVITRIFICATION.

TRANSDUCER FIG. 3

OF LOW DAMPING CHARACTERISTICS OUTPUT CIRCUIT GLASSES FOR TEMPERATURE-STABLE ULTRASONIC DELAY LINES Aug. 29, 1972 IN VE N TORS A T TORN E Y5.

MARGA FAULSTI'CK NORBERT NE UROTH BY W W*W m.oo5/- 2U -U.S. Cl. 106-53 United States Patent ABSTRACT OF THE DISCLOSURE Glass compositions for use in delay line assemblies having low temperature coefiicient of propagation time for ultrasonic waves, low mechanical damping, a transformation temperature of about 540600 C., and high acoustical impedance. Preferred compositions in percent by weight are as follows:

the total alkali metal oxide amounting to 0.7-1.8%, with the proviso that up to 2 of the wt. percent of BaO may be replaced by CdO, 'SrO, CaO, W0 A1 0 or a mixture of two or more thereof, for stabilization against devitrification.

BACKGROUND The invention relates to glasses for electromechanical delay lines which have a very low delay time temperature coefiicient. Furthermore, these glasses have a relatively low mechanical damping, so that the intensity of the signal is only slightly attenuated by passing through the delay line.

In an electromechanical delay line, the electrical signal is transformed by a piezoelectric transducer into sound vibrations. These pass through the glass body and at the end of the sound path they are transformed back into electrical vibrations by a second piezoelectric tranducer. The electrical signal at the output of the delay line is delayed by the amount of time which the sound takes to pass through the glass body. This travel time z is determined by the length L of the sound path and the velocity v of the sound in the glass, according to the equation z=L/ v.

In a number of applications it is required that the temperature coefiicient of time delay (T.C.) be very small, e.g.

2X per C.

3,687,697 Patented Aug. 29, 1972 'ice piezoceramic transducers, delay lines which have a delay time temperature coefiicient of this order of magnitude.

Two types of sound waves are possible in a solid: longitudinal waves and shear waves. In delay lines shear waves are preferred, because these waves have a lower velocity than longitudinal waves. The frequency, when measured, ranges around 5 megahertz.

Two factors are important in the attenuation of the electrical signal in passing through the line:

(a) The mechanical vibration damping of the glass; (b) The intimate fastening together of transducer and glass.

THE INVENTION The logarithmic decrement of the mechanical vibration damping (L.D.) in the case of the glasses described in this invention, at a frequency of l kilohertz, amounts to 035x 10- to 0.45 1O- that is, it is lower than it is in the special glasses of the prior art for this purpose. For example, in French Pat. No. 1,546,407 and copending application Ser. No. 687,099, filed Dec. 1, 1967, glasses are described in which 5=2 10 to 5 l0- and in German patent application p 16 96 064.8 and copending application Ser. No. 804,595, filed Mar. 5, 1969, glasses are described wherein 6=O.5 10- to 0.8 10- For (b) it is important that the glass be capable of good metallization. There are a number of processes for this purpose, e.g. vapor depositing and firing. 'For these processes it is desirable that the glass be able to withstand heating to high temperatures. The transformation temperature (Tg) of the glasses of the invention just cited, ranges from 540 to 590 C.

The velocity of shear waves (v,) is lower in the glasses of the instant invention and the acoustical impedance (A1.) is greater than in the case of the glasses hitherto described for temperature-stable ultrasonic delay lines which have a high softening temperature. Both of these factors represent technical improvements: the lower sound velocity signifies that the glass body can be made smaller, and the greater acoustical impedance means lower reflection losses in the passage of the sound waves from the glass to the transducer. The very low alkali oxide content in the glasses of the invention guards against mechanical after-effects.

The glasses of the invention have a small temperature coefficient of propagation time for ultrasonic waves, preferably for shear waves with a frequency of about 5 megahertz, with low mechanical dampening, transformation temperatures of about 540-600 C., and increased acoustical impedance. Preferred compositions are set forth in Table 2.

The total alkali metal oxide content amounts to 0.7 to 1.8%. For stabilization against devitrification, 2% of the BaO can be replaced by other alkali earth (SrO and CaO) or by CdO, W0 or A1 0 without substantially moditying the special properties which are important to the described application of the glass.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic showing of a delay line assembly; and

FIG. 2 and FIG. 3 show change in delay time versus temperature for compositions of the invention stated infra.

Referring to FIG. 1, a delay line medium 1 is installed in an ultrasonic delay line assembly, which is of conventioual construction. The delay line medium is outfitted with transducers 2 which are connected to imput circuit 3 and output circuit 4.

Examples In Table 1 there are listed a number of examples of glasses according to the invention. The chemical composition and the most important physical properties are stated:

TAB LE 1 Glass oxide:

o XlO/ C.(1O 60 C.

4.4 MHz. 1.2 0.8 1.5 1. 2 1.2

L.D.: (10g. decrementxw kHz. 0. 36 0. 41 0. 38 0. 37 0. 43

V,: Sound speed for shear waves, meters per sec 2, 722 2, 733 2, 742 2, 727 2, 730 Density (gJcmfi) 3. 58 3.58 3. 63 3. 57 3. 59 A.I.: Acoustical impedance,

10 kg./(m. sec.) 9.75 9. 76 9.96 9. 74 9. 80 Tg: Transformation temperature C.) 550 572 555 542 577 As can be seen from Table 1, the compositional ranges of the glasses of the examples consist essentially of:

These glasses also have the .foll'o' g properties:

Temperature coeilicient, 10 to '60 at 4.4 MHZ., 0.8 to 1.5 X 10- per C.; mechanical. damping in terms of logarithmic decrement at l kilohertz'of about 036x10- to O.43 10- sound speed for' 'shear'waves of 2722 to 2742 meters per second; density. of 3.57 to 3.63 grams/ cmfi; acoustical impedance of 9.74 10 936x10 kg./m. sec.); and a transformation temperature in the range of about 550 to 577 C. i'

FIGS. 2 and 3 show the eife-ct 0 I ,tempenature on the delay time in a delay line made from the glasses in the table and providing a 64 microsecond delay.

Production example The glasses of the invention are similar in type to known optical and art glasses, and they can be produced by procedures which are conventional for production of such glasses. In the instant example, the batch mixture consists of:

Amount weighed Pcrin, in kg., cent 100 kg. Oxide by wt. Raw material of glass SiOs 49. 599 KzCOa 1. 471 B2.(NO. )2 S. 726 E2100; 7. 263

ZnO 4. 907

CdO 2.007 P1330; 32. 362

The well-mixed batch is continuously fed into a conventional glass melting tanlg melted at about 1440? C. in about 16 hours, refined for about 14 hours, at about 1480- 1500 C. and until it is free of bubbles, and, at a viscosity between 300 and 500 poises (corresponding to temperatures of 1420 to 1360 C.), depending on the throughput, it is poured otf and worked directly into the desired molded objects or bars. In this example, the viscosity at pouring otf is about 6,000 poises. The melt can also be cast in blocks from which the desired objects can afterwards be pressed. The molded objects are annealed in accordance with conventional optical glass practice. The glass can also be produced in any smaller volume desired in platinum crucibles or appropriate ceramic crucibles.

A summary of the invention is contained in Table 2.

TABLE 2 Preferred range Optimum range Weight percent:

0-2 of the 1321.0

1 Units as in Table 1.

What is claimed is:

1. Glass having a low temperature coefiicient of the propagation time for ultrasonic waves, mechanical damp ening in terms of logarithmic decrement at 1 kilohertz of about 0.?,6 10* to 0.43X10 a transformation temperature in the range of about 550577 C. and high acoustical impedence, consisting essentially of the following chemical composition in percent by weight:

2. Glass according to claim 1, having the following properties:

temperature coefficien't, 10 to 60 C. at 4.4 MHz, 0.8 to 1.5 10- per 0.; sound speed for shear waves of 2722 to 2742 meters per second; density of 3.57 to 3.63 grams/cmfi; acoustical impedance of 9.74 to 9.96 X 10 kg./m. sec.). 3. Glass according to claim 1, characterized by the following chemical composition in percent by weight:

Si0 49.4 Na o 0.6 K 0 0.7 BaO 11.2 ZnO 3.8 PbO 340 4. Glass according to claim 1, characterized by the following composition in percent by weight:

5. Glass according to claim 1, characterized by the following composition in percent by weight:

SiO 48.4 K 1.0 BaO 11.5 ZnO 4.8 PbO 33.0 Sb 0 0.3 A1 0 1.0

6. Glass according to claim 1, characterized by the following composition in percent by weight:

SiO 48.5 K 0 1.0 BaO 10.5 ZnO 4.8 PbO 31.0 Sb O 0.3 CdO 2.0

7. Glass according to claim 1, characterized by the following composition in percent by weight:

SiO 48.4 Li O 0.2 K 0 0.3 BaO 11.5 ZnO 5.8 PbO 33.0 Sb O 0.3

8. Glass having a low temperature coefficient of the 6 propagation time for ultrasonic waves, mechanical dampening in terms of logarithmic decrement at 1 kilohertz of about 0.36X10- -0. 43 10 a transformation temperature in the range of about 550-577" C. and high acoustical impedance, consisting essentially of the following chemical composition in percent by weight:

SiO 48.5-49.7 Li O 0.0-0.2 arr-s 2 BaO 10.5-11.5 ZnO 3.1-5.8 PbO 3 l-34 Sb O 0.3-0.5

with the proviso that up to 2 of the wt. percent of BaO may be replaced by CdO, SrO, CaO, W0 A1 0 or a mixture of two or more thereof, for stabilization against devitrification.

9. Glass according to claim 8, having the following properties:

[temperature coefiicient, 10 to C. at 4.4 MHz., 0.8 to 1.5 10 per C.; sound speed for shear Waves of 2720 to 2745 meters per second; density of 3.58

to 3.63 grams/emf; acoustical impedance of 9.74 to 9.96 X 10 kg./m. sec.).

References Cited UNITED STATES PATENTS 2,762,713 9/1956 Davis et a1. 10653 FOREIGN PATENTS 1,807,831 8/1969 Germany 10653 1,118,422 7/1968 Great Britain 10653 132,387 5/ 1949 Australia 10653 TOBIAS E. LEVOW, Primary Examiner M. L. BELL, Assistant Examiner US. Cl. X.R. 333--30 UM'XHU $11155 m'rrchii x I-;. Ci-"JPt'IfEHlA/i 6 OE! (K)KE'W ECTEUN;

Patent NO. Dated August- 29 l "Ilwcntor(5) Marga Faulstich et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are. hereby corrected as'shown below:

1 H Col. ,3, lLne 75, chaoge b O to Sb O v Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,'JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

